| This dissertation researched the influence mechanism of some related disturbance types, e.g. excavation, ground loading and dewatering of confined aquifer on the existing metro structure and corresponding protective measures. The main works and conclusions are summarized as follows:(1) According to the practice project that the open cut of Xiqing Road Tunnel was constructed closely upon the existing tunnel of the operating Metro Line1, ABAQUS is applied to analyze the effect of excavation on the existing underlying metro tunnel. In order to control the excessive upheave of the tunnel and differential displacements at the deformation joints, some deformation control measures were proposed specially, including soil improvement alongside the existing tunnel, formation of protection hoop by slab and anti-floating piles, excavation in sections and timely suppression by heaped load, and the corresponding construction parameters were optimized. These results can provide evidence for the optimization of the construction design. The practical construction procedure was simulated dynamically based on the field monitoring data. Further on, the reasonability and the effectiveness of the deformation control measures mentioned above were analyzed by contrast analysis using numerical simulations.(2) The settlement induced by ground loading was monitored in the West Railway Station subway station of the Metro Line1. Besides, the deformation characteristics of structure were analyzed by field measurements and finite element method. The results show that the settlement curve is discontinuous at the structural deformation joint. Furthermore, the effects of many factors, e.g. the loading location, magnitude, area, buried depth of the structure and weather to pre-reinforce the soil around the deformation joints on the deformation of discontinuous metro station boxes were studied. It is found that the structural deformation joint can weaken the structure stiffness and increase the settlement and differential settlement of the structure.(3) Based on a certain pumping test, the soil parameters were derived by inverse analysis. On the basis of ensuring the feasibility of parameters, simulation was performed to find out the effect of dewatering of confined aquifer on the existing shield tunnel, and afterwards, the stress field of soil around the tunnel, the sectional distortion and internal forces and the longitudinal deformation of the tunnel were analyzed to study their influencing mechanisms. The results show that during the process of depressurization dewatering, the vertical total stress is almost constant whereas the horizontal total stress decreases. This phenomenon has the same effect with that both sides of the tunnel are subjected to tensile force, and leads to the aggravated flattening of tunnel, which has adverse effects on the load carrying capacity of tunnel section segments. On this basis, the research investigated the influence factors such as the position of the existing tunnel related to the artesian aquifer, the distance between tunnel and well, buried depth of the artesian aquifer and insertion depth of water-stop curtain in the artesian aquifer. It is indicated that dewatering has higher impact on the force of cross section and the longitudinal deformation of tunnel while the tunnel is located in the confined aquifer partly or completely. And dewatering has lower impact on the force of cross section but can cause the cross section have the tendency of twisting, while the tunnel is located in the aquiclude. However, the tunnel has a greater settlement along with the stratum while the tunnel is located in the upper aquiclude, which is adverse for the longitudinal deformation of tunnel. It should be pointed out that when the tunnel is close to the dewatering well, even there is a diaphragm wall cutting off the confined aquifer, the influence of dewatering on the longitudinal deformation cannot be neglected. |
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